Codon substitution model (codeml)

Question

[Chvatil]

Hello, I'm actually using codeml implemented into PAML and I wondered if there where not another codon substitution model than Goldman and Yang (1994) present into codeml?

I know tha there is another another one but I cannot manage to find it. Does anyone have the paper that talks of this model and/or the parameter in the command file in order to take this codon model instead of Goldman and Yang?

Thank you for your help.